In commonly owned, co-pending applications 07/666,816; 07/666,811; D667,100; 07/666,329; 07/666,327; 07/666,328; and 07/666,815, a rain tire having an aqua channel is described. The aqua channel is provided to prevent the build up of water in front of a tire as it rotates, by permitting the water to flow through the center of the tire. The build up of water in front of a tire, and the pressure exerted by said water, is the reason that tires sometime undergo hydroplaning in wet conditions. To illustrate this phenomenon, a device is needed through which one can observe the difference in the rolling properties between a tire with an aqua channel and a tire with a conventional tread.